# Choosing a Solar Panel for LoRa Nodes

Solar panel selection involves matching the panel's output to the node's energy needs while accounting for real-world efficiency losses, geographic location, and physical mounting constraints. This page covers panel technology, rating systems, derating factors, geographic sizing, and wiring configurations.

## Panel Technologies

<table id="bkmrk-technology-efficienc"> <thead> <tr> <th>Technology</th> <th>Efficiency Range</th> <th>Temperature Coefficient</th> <th>Low-Light Performance</th> <th>Physical</th> <th>Best Use Case</th> </tr> </thead> <tbody> <tr> <td>Monocrystalline silicon</td> <td>17 - 22% typical (up to ~24% for premium cells)</td> <td>−0.35% / °C above STC</td> <td>Good</td> <td>Rigid, glass-covered, aluminum frame</td> <td>Fixed installations, roof/pole mounts</td> </tr> <tr> <td>Polycrystalline silicon</td> <td>15 - 18%</td> <td>−0.40% / °C above STC</td> <td>Good</td> <td>Rigid, glass-covered, aluminum frame</td> <td>Budget fixed installations</td> </tr> <tr> <td>Amorphous silicon (thin-film)</td> <td>6 - 8%</td> <td>−0.20% / °C above STC</td> <td>Excellent (diffuse light)</td> <td>Flexible or glass, no frame</td> <td>Curved surfaces, low-light climates</td> </tr> <tr> <td>CIGS thin-film</td> <td>12 - 14%</td> <td>−0.32% / °C above STC</td> <td>Very good</td> <td>Flexible or rigid</td> <td>Curved surfaces where efficiency matters</td> </tr> </tbody></table>

**For most LoRa node deployments, monocrystalline panels are the correct choice.** Their higher efficiency means a smaller, lighter panel for the same power output - important when mounting on a mast or in a small enclosure. Thin-film flexible panels are useful when the panel must conform to a curved surface (conduit mast, cylindrical enclosure) or when severe vibration makes rigid glass panels impractical.

## Understanding Wp (Watt-Peak) Ratings

Panel power is rated in Watts-peak (Wp) at Standard Test Conditions (STC): 1000 W/m² irradiance, 25 °C cell temperature, AM 1.5 spectrum. Real-world conditions deviate from STC in several important ways:

### Real-World Adjustment Factors

Most rows below are losses (values below 1.0). One row — spectral mismatch in overcast — can slightly exceed 1.0 for amorphous panels (a small gain, not a loss). Do not blindly multiply every row together as if they were all losses; apply the spectral-mismatch row only to the panel technology it describes.

<table id="bkmrk-derating-factor-typi"> <thead> <tr> <th>Adjustment Factor</th> <th>Typical Value</th> <th>Explanation</th> </tr> </thead> <tbody> <tr> <td>Temperature (hot day)</td> <td>0.80 - 0.90</td> <td>Cell temp in direct sun reaches 50 - 75 °C. Monocrystalline loses ~0.35%/°C above 25 °C. At 60 °C: 1 − (35 × 0.0035) = 0.878.</td> </tr> <tr> <td>Dirt / dust / pollen</td> <td>0.90 - 0.97</td> <td>Uncleaned outdoor panel loses 3 - 10% annually. Clean panels every 6 - 12 months.</td> </tr> <tr> <td>Wiring and connection losses</td> <td>0.97 - 0.99</td> <td>Resistance in MC4 connectors and cable runs. Use AWG 10 - 12 for runs over 5 m.</td> </tr> <tr> <td>Charge controller harvest</td> <td>0.65 - 0.97</td> <td>This is the fraction of available panel energy delivered to the battery, not the controller's own conversion efficiency. PWM ties the panel to battery voltage, so a 18 V (12 V-nominal) panel charging a 13 V battery delivers roughly 65 - 75% of its rated energy — the mismatch is the loss, not the controller. MPPT tracks the panel's maximum-power point and delivers ~93 - 97%, recovering more when panel Vmp is well above battery voltage and in cold or low light. See Charge Controllers page.</td> </tr> <tr> <td>Partial shading</td> <td>0.50 - 1.00</td> <td>Even 5% shadow on a cell in a string can reduce total output by 50%+ (bypass diodes mitigate but don't eliminate).</td> </tr> <tr> <td>Spectral mismatch (overcast) — can exceed 1.0</td> <td>1.0 - 1.05 for amorphous; ~0.95 for mono</td> <td>A gain, not a loss, for amorphous: amorphous panels outperform mono in overcast because the diffuse-light spectrum favors their bandgap. Apply only to the matching panel technology.</td> </tr> <tr> <td>**Combined typical derating (MPPT, clean, no shade)**</td> <td>**0.70 - 0.80**</td> <td>Use 0.75 as a conservative planning factor</td> </tr> </tbody></table>

## Peak Sun Hours by US Region

Peak sun hours (PSH) is the equivalent number of hours per day at 1000 W/m² irradiance that delivers the same daily energy as the actual variable irradiance. It is the single most important geographic variable in panel sizing.

<table id="bkmrk-region-example-citie"> <thead> <tr> <th>Region</th> <th>Example Cities</th> <th>Annual Avg PSH</th> <th>Winter Worst-Month PSH</th> </tr> </thead> <tbody> <tr><td>Southwest Desert</td><td>Phoenix, Las Vegas, El Paso</td><td>6.0 - 7.0</td><td>4.5 - 5.5</td></tr> <tr><td>Mountain West</td><td>Denver, Salt Lake City, Albuquerque</td><td>5.5 - 6.5</td><td>3.5 - 4.5</td></tr> <tr><td>Southeast</td><td>Miami, Atlanta, Dallas</td><td>5.0 - 6.0</td><td>4.0 - 5.0</td></tr> <tr><td>Midwest / Great Plains</td><td>Kansas City, Minneapolis, Chicago</td><td>4.5 - 5.5</td><td>2.5 - 3.5</td></tr> <tr><td>Mid-Atlantic / Northeast</td><td>NYC, Philadelphia, Boston</td><td>4.0 - 4.8</td><td>2.0 - 3.0</td></tr> <tr><td>Pacific Northwest</td><td>Seattle, Portland, Eugene</td><td>3.5 - 4.2</td><td>1.5 - 2.5 (Seattle worst-month ~1.5)</td></tr> <tr><td>Alaska (Anchorage)</td><td>Anchorage</td><td>3.0 - 4.0</td><td>0.5 - 1.5</td></tr> </tbody></table>

Always size for the **worst-month PSH**, not the annual average, to ensure year-round operation. Use a single worst-month PSH value per location across the whole book; the values here are representative and should be confirmed against NREL PVWatts for your exact site.

## Panel Sizing Calculation

```

Required_Wp = Daily_Wh / (PSH_worst_month × overall_derating)

Example: 5.75 Wh/day node, Seattle (1.5 PSH worst-month winter), MPPT controller (0.95), other derating (0.85):
 Combined derating = 0.95 × 0.85 = 0.808
 Required_Wp = 5.75 / (1.5 × 0.808) = 5.75 / 1.212 = 4.74 Wp → use a 5 Wp panel (sized for the worst month; pair with several days of battery reserve for multi-day overcast)
```

## Panel Sizing by Latitude (Rule of Thumb)

<table id="bkmrk-latitude-%28%C2%B0n%29-panel-"> <thead> <tr> <th>Latitude (°N)</th> <th>Panel Wp Required per 1 Wh/day node load</th> <th>Notes</th> </tr> </thead> <tbody> <tr><td>25 - 30° (South Florida, Texas)</td><td>0.5 - 0.7 Wp</td><td>Year-round high sun</td></tr> <tr><td>30 - 37° (Southeast, Southwest)</td><td>0.6 - 0.9 Wp</td><td>Good solar resource</td></tr> <tr><td>37 - 42° (Mid-Atlantic, Midwest)</td><td>0.9 - 1.3 Wp</td><td>Moderate winter derating</td></tr> <tr><td>42 - 48° (New England, Northwest)</td><td>1.3 - 2.0 Wp</td><td>Poor winter sun</td></tr> <tr><td>48 - 65° (Northern US, Alaska)</td><td>2.0 - 5.0 Wp</td><td>Size for worst month or use large battery</td></tr> </tbody></table>

## Wiring: 5 V USB Charging vs 12 V Systems

### 5 V USB Charging (small panels, direct LiPo charging)

Panels rated 5 - 6 V open-circuit (e.g., 0.5 - 2 W "USB solar panels") are designed to pair with TP4056 or CN3791 LiPo charger ICs. These work only in full sun - the panel voltage drops below the charger's minimum input at partial cloud cover. Acceptable for *supplemental* trickle charging of small nodes but not reliable primary power. Note neither the TP4056 nor the CN3791 has a low-temperature charge cutoff, so for cold-climate builds add a BMS or charge controller with low-temp protection.

### 12 V Nominal Systems

Panels rated 18 V open-circuit (12 V nominal, e.g., 10 W, 20 W, 40 W monocrystalline) are the standard for serious solar deployments. These pair with a dedicated charge controller (PWM or MPPT) that regulates voltage down to the battery charge voltage. MC4 connectors are the industry standard for these panels.

### Series vs Parallel Configuration

<table id="bkmrk-configuration-effect"> <thead> <tr> <th>Configuration</th> <th>Effect on Voltage</th> <th>Effect on Current</th> <th>When to Use</th> </tr> </thead> <tbody> <tr> <td>Series (panels in series)</td> <td>Voltages add (2× 18 V = 36 V)</td> <td>Current stays same</td> <td>Higher voltage charge controllers; longer cable runs (less current = thinner wire)</td> </tr> <tr> <td>Parallel (panels in parallel)</td> <td>Voltage stays same</td> <td>Currents add (2× 5 A = 10 A)</td> <td>Same voltage system but need more current; partial shading (each panel has independent MPPT)</td> </tr> </tbody></table>

For small LoRa deployments (5 - 40 Wp), a single panel in direct connection to a 12 V charge controller is the simplest and most reliable approach.

## Recommended Panels for LoRa Deployments

Prices below are approximate and volatile, as of 2026-06-08; confirm against a current listing before buying.

<table id="bkmrk-panel-power-dimensio"> <thead> <tr> <th>Panel</th> <th>Power</th> <th>Dimensions</th> <th>Best For</th> <th>Approximate Cost</th> </tr> </thead> <tbody> <tr><td>Voltaic P110 (monocrystalline)</td><td>2 W, 6 V</td><td>132 × 91 mm</td><td>nRF52840 trickle charge, USB-C output</td><td>$25</td></tr> <tr><td>Newpowa NPA10-12MBK (mono)</td><td>10 W, 12 V nominal</td><td>340 × 235 mm</td><td>ESP32 nodes, primary solar</td><td>$20 - 25</td></tr> <tr><td>Renogy RNG-100D-SS (mono, compact)</td><td>100 W, 12 V nominal</td><td>~1062 × 531 mm</td><td>Pi gateway installations</td><td>$85 - 100</td></tr> <tr><td>Flexible mono ~50 W (verify SKU/datasheet)</td><td>~50 W, 12 V nominal</td><td>per datasheet</td><td>Curved mast mounting, marine</td><td>confirm current price</td></tr> <tr><td>Flexible CIGS ~30 W (verify SKU/datasheet)</td><td>~30 W, 12 V nominal</td><td>per datasheet</td><td>Curved enclosures, portable</td><td>confirm current price</td></tr> </tbody></table>